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SUMMARY:Effects of the Coulomb gap on electrical transport and magnetic
DTSTART:20110607T140000
DTSTAMP:20260924T173820Z
UID:d7944fa28290b2aedfd9728ef6b6ef141d6c0a004932ef2dd08455b3
CATEGORIES:Conferences - Seminars
DESCRIPTION:Mirko Bacani\, University of Zagreb\, Faculty of Science\, Dep
 artment of Physics\nWe have carried out a comparative experimental study o
 f the electrical conductivity and magnetic susceptibility of own-made poly
 aniline (PANI) pellets doped either with HCl or with dodecybenzenesulfonic
  acid (DBSA)\, the latter being a long molecule with surfactant properties
 . While the doping mechanism (protonation) is the same for the two dopants
 \, there are both differences and similarities in properties of the corres
 ponding doped PANI materials. X-ray diffraction patterns for PANI-HCl exhi
 bit signatures of partial crystallinity whereas PANI-DBSA is completely am
 orphous. Furthermore\, the dopant content in PANI-HCl is limited by the nu
 mber of available protonation sites\, whereas a stable two-phase system co
 nsisting of fully doped PANI-DBSA and excess DBSA molecules can form durin
 g the doping process. Nevertheless\, these two quite opposite types of dop
 ed PANI show remarkable similarities in temperature (T) dependences\, and 
 there are strong arguments in favour of the underlying physics being the s
 ame. For all samples\, we find that at low T is governed by the variable-r
 ange hopping (VRH) in a homogeneously disordered three-dimensional system 
 of coupled one-dimensional chains. Depending on the doping and correspondi
 ng disorder level\, the VRH exponents are either 1/2\, 2/5 or 1/4\, and at
  higher T in many of the samples we find the exponent 1 that signifies the
  nearest-neighbour hopping. All these exponents are predicted in a theory 
 of Fogler\, Teber and Shklovskii for the charge transport in coupled chain
 -like conductors\, and conditions for their appearance depend on disorder 
 and T. Changes from one exponent to another appear at crossover temperatur
 es T*\, where there are also noticeable features in (T). This coupling of 
 charge and spin is discussed in the spirit of kBT* being the thermal energ
 y which causes an enhancement of the density of delocalised (Pauli) spins 
 at the expense of localised (Curie) spins as T rises above T*.
LOCATION:PH L1 503
STATUS:CONFIRMED
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